10 



BULLETIN 34, UNITED STATES NATIONAL MUSEUM. 



the caudal regions of all the tailed orders, and are transient in the 

 tails of the larvae of the Salientia. Eemaius of the same are seen in the 



segmented dorsal muscles of the TJro- 

 dela, and the segmented median ven- 

 tral, or pubosternal muscles of the 

 tailed and tailless orders. Between 

 these median series of muscles extend 

 two layers, which support the sides 

 of the body cavity, the external and 

 internal oblique. In the Urodela the 

 external oblique is divided up at the 

 superior border into separate heads, 

 each of which arises from the extrem- 

 ity of a rib. Between the ribs is a 

 band of narrow longitudinal mus- 

 cles — theiutercostals — which are par- 

 allel to the dorsal muscles. Owing 

 to the modification of the skeleton 

 the dorsal muscles in the Salientia 

 are much modified, and form chev- 

 rons with the apex posterior. The 

 limb muscles are much like those of 

 higher vertebrata. 

 The heart of the Batrachia pos- 

 sesses three chambers, two auricles and one ventricle, and there is a 

 sinus venosus at the entrance of the vena cava. The bulbus arteriosus 

 is not muscular, and has a longitudinal valve or partial septum, or is 

 completely divided into two in the Proteida. In the Urodela there are 

 four aortic branches on each side, which are in the larval state branchial 

 arteries. As many veins return from the branchiae and unite above the 

 heart to form the aorta. In development to maturity the arteries be- 

 come connected with the veins by longitudinal vessels, the ductus botalli, 

 which complete the "aorta bows" where the branchial system disap- 

 pears. The first and last of these arches become subordinate, and 

 the intermediate on each side function as " aorta roots," whose union 

 forms the aorta. The carotid artery is a continuation of the ductus 

 botalli eonnecting the first and second bows, and the last bow is modi- 

 fied into the pulmonary vein. In the Proteida and Trachystomata 

 three aorta bows remain on each side, and the branchial arteries and 

 veins persist. In the Salientia three aorta bows remain, but the second 

 on each side only form the aorta, the first and last forming the carotid 

 artery and pulmonary vein. 



The venous system consists primitively, as in other vertebrata, of 

 two anterior and two posterior cardinal veins, which unite on each side 

 into a single transverse vessel, the Ductus cuvieri, which empties into 

 the sinus venosus. Subsequently two other pairs of longitudinal veins 



Fig. 2. Diagram of chondrocranium and cranial 

 nerves of Salamandra, from below (from Wie- 

 dersheim) . 



